The present invention relates to a motor control apparatus and control method for controlling speed or torque of an AC motor such as a synchronous motor and a reluctance motor.
The speed or torque of the AC motor such as the synchronous motor and the reluctance motor is controlled by current control or voltage control based on the rotor magnetic pole position. Recently, as a speed or torque control method of an AC motor, there have been suggested various magnetic pole position sensor-less control methods for controlling without sensing the rotor magnetic pole position by a position sensor (controlling by estimating the rotor magnetic pole position). For example, Japanese Patent Laid Open Publication No. 8-256496 discloses a technique for estimating a counter electromotive force (induced voltage) introduced from a motor voltage/current equation, from the applied voltage and motor current and estimating the rotor magnetic pole position from this estimated counter electromotive force.
However, in the aforementioned conventional technique, it is difficult to instantaneously estimate the direction of the counter electromotive force and there is a limit to enhance the response of the motor control system. That is, in the aforementioned conventional technique, in order to eliminate effect of the current pulsation attributed to inverter switching operation (noise caused by an external disturbance due to an inverter mixed in applied current), a noise filter is used to suppress the current pulsation. For this, in the aforementioned conventional technique, instead of using current differentiation in the motor voltage/current equation, the counter electromotive force is calculated by using an observer for adjusting the response by the feedback gain based on the observer theory. Accordingly, in the aforementioned conventional technique, it is difficult to instantaneously estimate the direction of the counter electromotive force and there remains a limit to enhance the response of the motor control system.
It is therefore an object of the present invention to provide a motor control apparatus and control method capable of controlling an AC motor with a high response without using a position sensor. Another object of the present invention is to provide a motor control apparatus and control method capable of controlling an AC motor having a salient pole with a high response without using a position sensor. Still another object of the present invention is to provide a motor control apparatus and control method capable of increasing the drive efficiency in the intermediate speed range to the high speed range of the drive system using the AC motor.
The present invention is characterized in that a counter electromotive force is estimated according to a current change of an AC motor and a current change by the applied voltage. Accordingly, the present invention includes a control apparatus controlling voltage applied to an AC motor from a power converter and having current change sensing means for sensing a current change of the AC motor, current change calculation means for calculating a current change by the voltage applied to the AC motor from the power converter, and counter electromotive force estimating means for estimating a counter electromotive force according to the current change sensed by the current change sensing means and the current change calculated by the current change calculation means. When the AC motor is a synchronous motor having a salient pole, the current change calculation means calculates a current change by the voltage applied to the synchronous motor from the power converter and also calculates a current change by the inductance changed by rotation of the synchronous motor.
Moreover, the control apparatus has correction means for correcting the current change calculated by the current change calculation means according to the input voltage of the power converter. The current change sensing means senses a current change at a timing when the affect of current change changed by the power converter switching operation is removed. The current change calculation means calculates a current change by receiving an applied voltage instruction calculated before sensing the current change by the current change sensing means.
According to the present invention, the magnetic pole position of a rotor of an AC motor is estimated according to an estimated counter electromotive force direction and voltage applied to the AC motor from the power converter is controlled according to this estimated magnetic pole position.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.